Preparation of esters



Patented Oct. 1943 t UNITED S ATES PATENT OFFICE Donald :ssi gnor to E. L dlLPont de Nemours & Company, -Wil;- mington, Del., a corporation of nelawiarel No Drawing.

Application November 23,1940, Serial N0. 366,880

s (.01. mam) An object of the presentinvention is toprovide a process for the esterification of'hydroxyacetic acid, wherein part or all of thejwat'er of eSteri flcation is removed prior to ,esterification; A further object of the invention is to provide a'process wherein hydroxyacetic acid, fromwhich the free and a-substantial portion of the combined water has been withdrawn, is esterified 'under superatmospheric pressures. Otherobjects and advantages of the invention willhereinafter appear.

Due to the bifunctional nature of hydroxyacetic acid, several types ofproductscanresult from its dehydration, for example, the elimination of 1 mole of water from the alcoholichydroxyl groups of 2 moles oi the acid gives diglycolic acid, which may further lose water to form a ring. compound, diglycolic anhydride. The elimination of rl'mole of water fromthecarboxyl groups of 2 moles of. the acid giveshydroxyacetic anhydride, aud o! 2 moles of water from 2 moles of the acid by esterifica'tion o1" the h'ydroxyl" groups with the carboxyl groups; a ring compound, 2;5-diketo-1,4 dioxane orv dlglycolide'i Furthermore, the carboxyl groups of lmoleoi' the acid may react withthe hydroxyl groups of'another moleof the acid-with elimination of 1 mole f-water to give hydroxyacetoxyacetic acid. The

latter compound may further react with' -more hydroxyacetic acid or with itself by esterification of carboxyl groupsan'd/or hydroxyl groups with hydroxyl groups and/orcarboxyl groups to ive 'a simple polyester. The latter process ma be repeated consecutively, the carboxyl group of a low molecular weight polyester reacting with the hydroxylgroup orhydroxyacetic acid or a low molecular weight polyester therefrom. and so on; until a longjchaln' linear poly ester is formed. In' the samemannerjtwo or, more low molecularweight polyester molecules can react to form higher molecular weight polyesters. Fin a1- 1y, at anypoint in the formation of the polyester the'carboxyl group at oneend of said polyester may esterify the hydroxyl group at the other end to form a large ring compound. The elimination ofwater, therefore, from hydro xyacetic acidme produce, as is evidencedbythe above'reactions, a number oi compounds dependent uponthe manner in which the elements of water unite. under the'random conditions or molecular orientation prevalent in thejreaction mixturegiDehydrated hydroxyacetic acid may contain the above typesbf reaction products invarying proportions. t

It has been; found" that if hydroxyacetic acidfis thus dehydratedyand then subjected tofesterification,"go0d yields of the ester win resultQthe rate of the reaction is considerably greater than that-of the undehydrated hydroxyacetioacid and the throughputof a given apparatus considerably augmented. These advantages have particular significance when the reaction is conducted un-' derpressure inasmuch as the greater conversion of ester at equilibrium makes it possible in a batch or continuous 1 process to obtain considerably: greater capacity from a, given equipment.

I Moreover, it has been found that it is very ditficult to remove water from an ester of glycolic acidtand'in addition a partially dehydrated glycolic acid is less corrosive than th aqueous acid.

Furthermore, it has been founddesirable toremove as much of'the free and combined water as possible fromthe acid before mixinglt with the alcohol, not'only'in order to decrease the quantity of materials to be handled, but'also to shift the quilibrium of the esterification 7 reaction as far as possible ltoward the lalkyl hydroX-yacetata "While it appears thata small change inthe amount 'ofdehydration does not appreciably effect the results, on the'other hand, too great'an amount of dehydration introduces handling dif-' ficulties; if continuous operation is contemplated, due/to the solidification of'the polymers. "Dehydration to a calculated acidity between 104% and 113 %"'h 'a's been found to give satisfactory results with dehydration to 110% acid as the reccmm'enaea value for 'esteriflcation by a'continuous process. It is further advisable when using the'dehydrated acid above 106% to keep it above approximately 7550. until the alcohol ha been added whenit maybe cooledfto around 45 0. if desired; Nevertheless, if the esterification is,

effected by a batchpro'cess; fully dehydrated acid.

may be used andthe esterification effected between the; alcohol and the molten dehydrated acid, such reactions being conducted under eledehydrated acid'in a l'osed vessel, the resulting mixture preheated to atemperaturebetween 200 and 230?Cland held at the selected temperature V for from 10 to 'rninutes," the pressurefbeing maintained during esteriflcation at between 200 and;1,000"pounds per square inchy-or, if desired, acto 'nqus essur s m d- LQWer temperatures may be used, say down to -C.

or lower with a somewhat lower reaction rate. If high boiling alcohols are employed, such as ethylene glycol and glycerine, elevated pressure need not be used. The pressure is then rapidly released, whereupon the unconverted alcohol is flashed off, and the ester recovered by fractional distillation. If it be desired to speed up the reaction, esterifica-tioh catalysts such as sulfuric acid, hydrochloric acid, and the like may be used, but the reaction proceeds satisfactorily under the conditions given without a catalyst.

If the dehydration of the hydroxyaceticacid-is continued until a polyglycolide is made containing substantially no free or combined watei, the

reaction conditions differ somwlifit those used for treatment of the partially deiiydiatea acid. Glycolide is, at room temperatures, a hard solid, but when the temperature is raised vein the neighborhood of 215 C. it is converted to the molten state. that the glycolide can be esteriiied directly with an alcohol in the presence or in the absence off an;estei -ification catalyst. j Intne reaction f the fully dehydrated acid; it 'has been found advantageous to conduct the esterification nnderpres sures in excess ofatmospheric ahd geherally at pressures ranging between 100 and 5,000 pounds m ar l c maybe em loyed- The alcohol is added preferably instoichiot a x e fin. a e et si i e 21%. 6195 thereof per mole of the partiallylor completely ra eda i An ohqllvsl be 4. i the esterification, such, for example as methanol, ethanol, nand iso-pjropanol, nand isobutano-l, vt l and h r, tra ht and b a hed, .e 'a alcohols as we1l as the mixtures or partioular fractions of the mixtures of alcohols obtaine cl hy the r eeene n carb pace men stures of alcohols obtained from oleiines arorniatic alcohols such as benzyl alcohol, p'olyhydric alcohols such as glycol glyceroletc as well as the unsaturated alcohols such as oleyl alcohol, allyl alcohol and the like;

While this invention is primaifi ly directed t esterification of the partiallyor'f ully dehydrated hydroxyacetic acid, it may likewise be used for converting one ester to another by so-called alcoholysis, When so employed the initial -heating (in this case, of an esterof hydroxyaeetio acid) removes alcohol and not water and the subsequent treatment with an alcohel is alcoholysis rather than esteritigation. I f, howe ver', an ester is heated for a considerable period of time a glycolide will result andgdn effect its treatment with an alcohol would then be strictl esterification. V w v 1 Examples will now be given illustrating prefer-red embodimentsot the invention. Parts are by weight unless otherwise indicated.

Example 1 .Hydroxyacetic acid was. dehydrated ate temperature b'etwe napproxifnately 180 and 200 C. until an acid was obtainedwhich analyzed approximately l hydroxyactic acid. The resulting dehydrated acid was c ntacted with methanol in the race e; '1 .3 ine; of methanol per mole of the dehydrated acid at a temperature of 210 and under a pressuie or approximately jsto pbiiiids per sqiiar inch, the time or contact being approximately Methyl hydroxyacetate wasi'ecovered by distillation fr:oin the crude reaction product in ayield er approximately 68%. V I i i t me. pear nn e sis fi 6 h drated by distillation under atmospheric pressure and at a temperature of approximately 180 C.

In this state, it has beer'r found to give a acid (calculated as hydroxyacetic acid). This product together with isobutanol in the ratio of approximately 1.3 moles of isobutanol per mole of the dehydrated acid was charged at the rate of 30 pounds per hour into a falling film converter, such as is described in the copending application of F. W Pardee, S. N. 301,190, filed October 25, I939, wherein the pressure was maintained at approximately 500 pounds per square inch and the temperature at approximately 225 C. The time of contact in the converter was in the order of 10 minutes and there was recovered from the crude reaction piddu'ct isebalgyl'h-ydroxyacetate in a yield of ape ef me r a i'afdmpl' 3i"'Hydroxyacetic acid was dehydrated by distillation under atmospheric pressure to give an acid of between 110 and calculated as hydroxyacetic acid and the remainder' er the water was then removed by distillatiogi; under a pressure of approximately l00 min; ofmercuryandat atemperature of 22019. during a period ofapprgximately one hour. The resulting dehydrated and was heated in an autoclav the molten state and at amiio nnateiy 2 10 C. methanol was rereea in to give l,3 'm'oles of methanol per more. of the acid. Unuere piessine'cr approximately 500 pounds persquare mest e e-etc was continu'ed' 'foi absten- 1 donates. The esterified pro uct, we; sedate *'d e s tha oetjatei, consisted of better than :60?? methyl hydroxyacetate.

fiaite n it es writhin e ere are detainee by arrest s"tei"i'fi c'atlon of the partially'or fully denia ateuh'yarcsyaeetrc' 'a'ci'd, while it the esrers'ar tttamen by arebhorysrs, catalysts such as: the alkali me al and marine earth metal algoxifds may be employed;

I "claim:

1 A process for the preparation of methyl hydrox yacetate which comprises dehydrating hydrokyalcetic acid until it analyzes between 104% and 110% hydroxyadetic acid, preparing a mixture consisting of the th'u's dehydrated acid with a stoichionletric excess 'of methanol, and ef'-' fe'ctlng th'e esterification at 'a pressure between 200 and 1 000 pounds per square inch and at a temperature between 200 and 230 G.

2. A process-for the preparation of methyl hydroxyacetate which comprises dehydrating hydroxyacetic acid until it analyzes approximately 110% hydroxyacetic acid, preparing a mixture consisting of the thusdehydrated acid with a stoichiometri cal excess of methanol, but not-'more than l i moles of methanol per mole ofthe dehydrated acid, and subsequently reacting the resulting mixture at a temperature between 200 and 2301C; and under a pressure between 200 and 1,000 pounds persquare-inch.

3. process for the preparation of methyl hydroxyacetalte which comprises dehydrating hydroxyacetic acid until it analyzes approximately 110%; hydroxyacetic acid, preparing a mixture consisting of the thus dehydrated acid with methanol in the ratio of 1.3 moles of methanol per more or the I dehydrated acid and subsequently reacting the resulting mixture at stemperature or 2102' o. and unae'riapressure oi the pounds "per square inch.

4. A pre eessror the deafened or sotutyl hydroxyacetate which comprises dehydrating hydroxya'ct'ic acid 1mm it analyzes approximately" 110% eyew tness and; preparing arma ure consistingof the time dehydrated and with a stoichiometrlcal excess 01. isobutanol but not more than 1.4 moles of isobutan'ol per mole' of the dehydrated acid and subsequently reacting the resulting mixture at a temperature between 200 and 230 C. and under a pressure between 200 and 1,000 pounds per square inch. p

5. A process for the preparation of ethyl hydroxyacetate which comprises dehydrating hydroxyacetic acid until it analyzes approximately 110% hydroxyacetic acid, preparing a mixture consisting of the thus dehydrated acid with a stoichiometric excess of ethanol, but not more than 1.4 moles of ethanol per mole of thedehydrated' acid, and subsequently reacting the resulting mixture at a temperature between 200 and 230 C. and-under a pressure between 200 and 1,000 pounds per square inch.

6. A process for the preparation of an alkyl hydroxyacetate which comprises dehydrating hydroxyacetic acid until it analyzes between approximately 104 and 113% hydroxyacetic acid, 7

preparing a mixture consisting of the thus dehydrated acid with a stoichiometrical' excess of an'alcohol, and subsequently reacting the resulting mixture at a temperature between '200 and 230 C. and under a pressure between 100 and 5000 pounds per square inch.

' DONALD J. LODER. 

